The invention relates to a method for transmitting data for a security device, in particular for access authorization systems and/or driving authorization systems of a motor vehicle, in which data are transmitted over the air from a transmitter unit to a receiver unit, and a system for activating and/or deactivating a security device.
The publication WO 92/18732 of this generic type discloses a device for operating a door-lock system and/or alarm system in which the user carries a movable transmitter in which an encoded information item for activating or deactivating the aforesaid security devices is stored. Arranged in the motor vehicle is a receiver device which receives the high-frequency signal transmitted over the air by the transmitter, and compares it with a reference code which is stored in it. When these information items correspond, a signal is output to the door-lock system and/or alarm system.
The transmitter signal is transmitted only if the person carrying the transmitter is at a predefined distance from the motor vehicle, which distance lies within the range of the transmitter.
The transmitter is activated here by means of a signal from the receiver without manual intervention of the user. When the high-frequency radio link is used, the information item is modulated onto a carrier frequency which is in the megahertz or gigahertz range.
However, the advanced telecommunications possibilities also permit the identification code to be interrogated in a contactless fashion over relatively large distances, unnoticed by the vehicle owner, and to be transmitted to the motor vehicle without the vehicle owner being aware of it.